ecdsaSignatureAlgorithm function
The ecdsa-with-SHAx AlgorithmIdentifier for hash - a bare OID, with no
parameters, exactly as RFC 5758 ยง3.2 specifies for ECDSA.
Implementation
Uint8List ecdsaSignatureAlgorithm(crypto.Hash hash) =>
derSequence([derOid(_ecdsaSignatureOid(hash))]);